1. Field of the Invention
The invention relates to an ink jet maintenance system for a full width array (FWA) thermal ink jet printer. The system has a translatable maintenance station carriage assembly including priming nozzles, wipers and drop detection hardware for translating across the width of the front nozzle face of one or more fullwidth array (FWA) printbars. The FWA printbars are pivotally articulated between a print position and a maintenance position. An articulating cap assembly facilitates capping of printbar nozzles when the maintenance station carriage assembly is at a home position outside the edge of the printbar. When the cap assembly moves away from the printbar, a free space area is provided that allows unrestricted translation of the maintenance station assembly.
2. Description of Related Art
Maintenance subsystems in thermal ink jet printers have the following functions: purging, wiping, priming, drop sensing and capping. Viscous ink usually accumulates at the end of nozzles within a moving printhead or a stationary nozzle array. The accumulation is caused by evaporation of volatile components from the ink/air interface at the end of the nozzle.
Purging involves firing waste drops of ink to eject any such viscous ink at the end of the nozzle. Purging is required during interdocument zones due to the need to keep unused jets "fresh" during long document runs. Because there is a need for large amounts of purging over time, a waste gutter under the printbars is required to accommodate the waste ink. Alternative accommodation for waste ink can include spitting through openings in the paper transport belt or purging onto the belt and subsequent cleaning.
Wiping operations are usually performed by a wiper blade that moves relative to the front face of the nozzles to wipe off any residual ink from the front face of the nozzles. Vacuum priming usually involves applying a vacuum to the nozzle ends at the front face of the printhead or printbar. Capping of the ends of the nozzles involves placing a cap, consisting of an interior cavity and a perimeter seal, around the printer nozzles providing an airtight seal with the front face, keeping the nozzles from drying out. A preferred construction of a cap is that of a humidified cap having a maintenance fluid, water plus a biocide, contained within the interior cavity of the cap.
Drop sensing mechanisms can also be provided. Drop sensors are used to detect the presence of the drops after maintenance wiping and priming functions. Electronic circuitry may also be provided to sense the current drawn by the thermal ink jet heaters. If the current to the heater is within acceptable limits, the element is assumed to be electrically good and a missing drop is assumed to be due to a nozzle blockage. In this case, a second or subsequent maintenance cycle is initiated, perhaps at a reduced maintenance carriage speed. This cycle is repeated until all nozzles are firing drops or until a predetermined number of cycles has been completed. In the latter, a service action may be issued. A service action may also be issued if the current detector detects an open circuit heater or excess current draw.
Most known maintenance stations for full width array printers are located opposite a printbar array, but have an endless belt located between the maintenance station and the front nozzle face of the printbar array. This usually requires at least one opening in the endless belt. The opening must be aligned with the nozzle face and the belt must be stopped to allow initiation of maintenance operations.
Examples of these types of known art are U.S. Pat. Nos. 5,051,761 and 5,117,244, both assigned to Xerox Corporation. These references utilize a fixed FWA array and both have disadvantages. One has limited maintenance station component sizing and operation due to space restraints within the endless belt structure. The other cannot provide wiping or vacuum priming and requires use of the endless belt and magnetic forces to provide capping.
There is a need for a maintenance system that can provide reliable maintenance of a printbar or multiple printbars such as a full-width array (FWA) printbar. There also is a need for a maintenance system that can translate across a front face of a FWA printbar without interfering with a document platen, belt or any other structure that is located in front of the printbar during normal printing operation.